1. Field of the Invention
This invention relates to an adhesive sheet, and in particular relates to an adhesive sheet, which is used by being stuck onto a display device such as CRT or LCD, for example.
2. Description of the Prior Art
In the conventional display devices such as CRT or LCD, a protective film, which is constructed in the form of an adhesive sheet, is being stuck. Such an adhesive sheet includes a base material film, and the base material film is normally formed of a resin material. In the case where such a base material film is formed of a material such as PET (polyethylene terephthalate), which is likely to generate gas due to decomposition when irradiated with ultraviolet light, a blister will be produced at the adhesive layer due to bubbles of the generated gas.
Further, in recent years, there are known adhesive sheets having a laminated film, which is formed by laminating a thin film on a base material film of the adhesive sheet. Examples of such a laminated film include an AR (anti-reflection) film and a multi-layered film, which is formed by laminating a plurality of thin films made of metal or metal oxide. These laminated films have very low gas-permeability due to existence of the thin film, so that gas generated by decomposition of the base material film or the like is difficult to pass the adhesive layer and then vaporize. With this result, gas which is generated in the adhesive layer or at the boundary surface between the adhesive layer and the base material film is likely to accumulate, and therefore a blister is produced in the adhesive layer due to bubbles of the generated gas.
In order to solve the problem described above, there is known an anti-blister type adhesive sheet, which uses an adhesive component in which a macro-monomer is mixed. This type of adhesive sheet can effectively prevent a blister from being produced in the adhesive layer for the case where only the base material film is provided. However, this adhesive layer can not prevent the formation of such a blister sufficiently for the case where a thin film is laminated on the base material film as described above.
In view of the above problem, it is an object of the present invention to provide an improved adhesive sheet, which can exhibit an excellent anti-blister characteristic without susceptible to the property of the base material.
In order to achieve the above object, the present invention is directed to an adhesive sheet which comprises a base material; and an adhesive layer which contains, as its main component, an adhesive component and a curing component, wherein the adhesive layer has a storage modulus (dynamic modulus) in which a ratio of storage modulus G2xe2x80x2/G1xe2x80x2 of the adhesive layer lies within the range of 1.2 to 50, wherein G1xe2x80x2 is a storage modulus of the adhesive layer before curing at a temperature of 25xc2x0 C. and at a frequency of 1 Hz, and G2xe2x80x2 is a storage modulus of the adhesive layer after curing at a temperature of 25xc2x0 C. and at a frequency of 1 Hz.
According to the invention as described above, it is possible to provide an adhesive sheet which can exhibit excellent anti-blister effect irrespective of properties of the base material and possess high adhesive strength.
In the present invention, it is preferred that the base material has gas-impermeability. Further, it is also preferred that said base material includes at least one thin film.
Further, in the present invention it is also preferred that the weight-average molecular weight of the adhesive component is 300,000 to 3,000,000. Preferably, the adhesive component contains alkyl esters of acrylic acid or alkyl esters of methacrylic acid as its main composition.
Furthermore, in the present invention, it is preferred that the curing component is the type, which is to be cured by irradiation with radiation. Further, it is preferred that the curing component contains acrylic-based monomer or oligomer. In this case, it is preferred that the acrylic-based monomer or oligomer is a reactive monomer or oligomer, which has acryloyl group.
Moreover, in the present invention, it is also preferred that the amount of the curing component is 0.05 to 50 parts by weight with respect to 100 parts by weight of the adhesive component.
Another aspect of the present invention is directed to an adhesive sheet for use on a display device, comprising:
a base comprising a base film having a first side and a second side opposite to the first side and at least one thin film provided on the first side thereof; and
an adhesive layer provided on the second side of said base film for stacking the adhesive sheet onto the display, said adhesive layer containing, as its major component, an adhesive component and a curing component, wherein the adhesive layer has a storage modulus (dynamic modulus) in which a ratio of storage modulus G2xe2x80x2/G1xe2x80x2 of the adhesive layer lies within the range of 1.2 to 50, wherein G1xe2x80x2 is a storage modulus of the adhesive layer before curing at a temperature of 25xc2x0 C. and at a frequency of 1 Hz, and G2xe2x80x2 is a storage modulus of the adhesive layer after curing at a temperature of 25xc2x0 C. and at a frequency of 1 Hz.
According to the invention as described above, it is possible to provide an adhesive sheet which can exhibit excellent anti-blister effect when it is used on a display device irrespective of properties of the base material, and the adhesive sheet possesses high adhesive strength.
The above described and other object, structure and advantage of the present invention will be more apparent when the following description of the preferred embodiment will be considered taken in conjunction with the appended drawing.